The invention relates to adaptive channel equalizers for digital television receivers and, more particularly, to overcoming the effects of co-channel NTSC interference upon the updating of filter coefficients for such equalizers.
The updating of filter coefficients for an adaptive channel equalizer included within a digital television (DTV) receiver is accomplished by one of two known types of adaptation method or by a combination of these two adaptation method types. The first type of adaptation method is referred to as the training signal type. The second type of adaptation method is referred to as the decision-directed type. Both types of adaptation method can be disrupted by demodulation artifacts of NTSC co-channel interference accompanying the demodulated baseband symbol coding recovered by the DTV receiver.
In a digital television receiver embodying the invention the filter coefficients of an adaptive equalizer are adjusted by a decision-feedback method using an error signal extracted from baseband symbol coding in which artifacts of NTSC co-channel interference have been suppressed. The adaptive equalizer is followed in cascade by a filter for suppressing unwanted demodulation artifacts of NTSC co-channel interference. The decision-feedback signal is derived from the response of the filters for suppressing unwanted demodulation artifacts of NTSC co-channel interference. This avoids erroneous adjustments of the filter parameters of the adaptive equalizers that results when the decision-feedback signals are accompanied by demodulation artifacts of carrier components of the NTSC co-channel interference.